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Globular clusters are dense collections of hundreds of thousands to millions of stars found orbiting around galaxies, including the Milky Way. Unlike galaxies, they show no evidence of dark matter, and their stars are unusually uniform in age and chemical composition – traits that have left scientists debating their formation since their discovery in the 17th century.

Surrey researchers used ultra-high-resolution simulations that can trace the Universe’s 13.8-billion-year history in unprecedented detail, allowing them to watch globular clusters form in real-time within their virtual cosmos, called EDGE. The simulations find multiple pathways for their creation and, unexpectedly, the emergence of a new class of star system – “globular cluster-like dwarfs” – that sits between globular clusters and dwarf galaxies in terms of their properties.

Dr Ethan Taylor, Postdoctoral Research Associate at the University of Surrey’s School of Mathematics and Physics and lead author of the study, said:

“The formation of globular clusters has been a mystery for hundreds of years, so being able to add additional context surrounding how they form is amazing. We were able to do this in our EDGE simulations without having to add anything special to make them appear, and it just brings the simulations that extra level of realism. Additionally, being able to find a new class of object in the simulations is very exciting, especially since we have already identified a handful of candidates which exist in our very own Milky Way.”

Working in collaboration with Durham University, the University of Bath, the University of Hertfordshire, Carnegie Observatories and the American Museum of Natural History in the USA, Lund University in Sweden and the University of Barcelona in Spain, researchers used the UK’s DiRAC National Supercomputer facility to run the EDGE simulations over several years. To put the scale into perspective, if the largest simulations were run on a standard or high-end laptop, they would take decades to complete. These simulations not only recreated realistic globular clusters and dwarf galaxies but also predicted a previously unknown class of object.

Conventional dwarf galaxies are typically dominated by dark matter, with around a thousand times more of the mysterious substance than stars and gas combined. However, the newly identified ‘globular cluster-like dwarfs’ appear similar to regular star clusters when observed, yet still contain a significant amount of dark matter – meaning telescopes may have already found them in the real universe and classified them as regular globular clusters. This small difference would place them in a unique position to study both dark matter and cluster formation.

Several known Milky Way satellites, such as the “ultra-faint” dwarf galaxy Reticulum II, are likely candidates. If confirmed, they could become prime sites for the search for pristine, metal-free stars born in the early Universe and new locations to test models for the ever-elusive “dark matter.”

Professor Justin Read, Chair of Astrophysics at the University of Surrey, said:

“The EDGE project set out to build the most realistic simulation of the very smallest galaxies in the Universe – one that could follow all 13.8 billion years of its history while still zooming in on the tiny details, like the blast from a single exploding star. It took years to run on the UK’s DiRAC National Supercomputer, but the payoff has been extraordinary. At a resolution of just 10 light years, fine enough to capture the effects of individual supernovae, we’ve been able to show that globular clusters can form in at least two different ways, both without dark matter.”

The next step is to confirm the existence of these globular cluster-like dwarfs through targeted observations with telescopes, including the James Webb Space Telescope and upcoming deep spectroscopic surveys. If they do, it could give astronomers new ways to test dark matter theories and offer some of the best chances to find the Universe’s very first generation of “metal-free” stars.

White dwarfs may still host habitable planets. Conditions like tidal heating and migration shape their potential for life.

The Sun will eventually die. This will occur when it exhausts the hydrogen fuel in its core and can no longer generate energy through nuclear fusion. While this stage is often imagined as the final chapter for the solar system, it could instead mark the beginning of a new evolutionary phase for the objects that remain within it.

When stars similar to the Sun die, they expand dramatically during what is known as the Red Giant phase. Their radius increases, their surface becomes cooler and redder, and their weakened gravity can no longer hold on to the outer layers. As much as half of the star’s mass can escape into space, leaving behind a dense stellar remnant called a white dwarf.

I am a professor of astronomy at the University of Wisconsin-Madison. In 2020, my colleagues and I discovered the first intact planet orbiting around a white dwarf. Since then, I’ve been fascinated by the prospect of life on planets around these, tiny, dense white dwarfs.

Searching for signs of life

Astronomers search for extraterrestrial life by monitoring planets as they pass in front of their host stars from our line of sight. With the star’s light shining through the planet’s atmosphere, scientists can apply basic physical principles to determine what kinds of molecules are present.

In 2020, researchers realized they could use this technique for planets orbiting white dwarfs. If such a planet had molecules created by living organisms in its atmosphere, the James Webb Space Telescope would probably be able to spot them when the planet passed in front of its star.

In June 2025, I published a paper answering a question that first started bothering me in 2021: Could an ocean – likely needed to sustain life – even survive on a planet orbiting close to a dead star?

A universe full of white dwarfs

A white dwarf has about half the mass of the Sun, but that mass is compressed into a volume roughly the size of Earth, with its electrons pressed as close together as the laws of physics will allow. The Sun has a radius 109 times the size of Earth’s – this size difference means that an Earth-like planet orbiting a white dwarf could be about the same size as the star itself.

White dwarfs are extremely common: An estimated 10 billion of them exist in our galaxy. And since every low-mass star is destined to eventually become a white dwarf, countless more have yet to form. If it turns out that life can exist on planets orbiting white dwarfs, these stellar remnants could become promising and plentiful targets in the search for life beyond Earth.

But can life even exist on a planet orbiting a white dwarf? Astronomers have known since 2011 that the habitable zone is extremely close to the white dwarf. This zone is the location in a planetary system where liquid water could exist on a planet’s surface. It can’t be too close to the star that the water would boil, nor so far away that it would freeze.

The habitable zone around a white dwarf would be 10 to 100 times closer to the white dwarf than our own habitable zone is to our Sun, since white dwarfs are so much fainter.

The challenge of tidal heating

Being so close to the surface of the white dwarf would bring new challenges to emerging life that more distant planets, like Earth, do not face. One of these is tidal heating.

Tidal forces – the differences in gravitational forces that objects in space exert on different parts of a nearby second object – deform a planet, and the friction causes the material being deformed to heat up. An example of this can be seen on Jupiter’s moon Io.

The forces of gravity exerted by Jupiter’s other moons tug on Io’s orbit, deforming its interior and heating it up, resulting in hundreds of volcanoes erupting constantly across its surface. As a result, no surface water can exist on Io because its surface is too hot.

In contrast, the adjacent moon Europa is also subject to tidal heating, but to a lesser degree, since it’s farther from Jupiter. The heat generated from tidal forces has caused Europa’s ice shell to partially melt, resulting in a subsurface ocean.

Planets in the habitable zone of a white dwarf would have orbits close enough to the star to experience tidal heating, similar to how Io and Europa are heated from their proximity to Jupiter.

This proximity itself can pose a challenge to habitability. If a system has more than one planet, tidal forces from nearby planets could cause the planet’s atmosphere to trap heat until it becomes hotter and hotter, making the planet too hot to have liquid water.

Enduring the red giant phase

Even if there is only one planet in the system, it may not retain its water.

In the process of becoming a white dwarf, a star will expand to 10 to 100 times its original radius during the red giant phase. During that time, anything within that expanded radius will be engulfed and destroyed. In our own solar system, Mercury, Venus and Earth will be destroyed when the Sun eventually becomes a red giant before transitioning into a white dwarf.

For a planet to survive this process, it would have to start out much farther from the star — perhaps at the distance of Jupiter or even beyond.

If a planet starts out that far away, it would need to migrate inward after the white dwarf has formed in order to become habitable. Computer simulations show that this kind of migration is possible, but the process could cause extreme tidal heating that may boil off surface water – similar to how tidal heating causes Io’s volcanism. If the migration generates enough heat, then the planet could lose all its surface water by the time it finally reaches a habitable orbit.

However, if the migration occurs late enough in the white dwarf’s lifetime – after it has cooled and is no longer a hot, bright, newly formed white dwarf – then surface water may not evaporate away.

Under the right conditions, planets orbiting white dwarfs could sustain liquid water and potentially support life.

Searching for life on white dwarf worlds

Search for life on planets orbiting white dwarfs
Astronomers haven’t yet found any Earth-like, habitable exoplanets around white dwarfs. But these planets are difficult to detect.

Traditional detection methods like the transit technique are less effective because white dwarfs are much smaller than typical planet-hosting stars. In the transit technique, astronomers watch for the dips in light that occur when a planet passes in front of its host star from our line of sight. Because white dwarfs are so small, you would have to be very lucky to see a planet passing in front of one.

Nevertheless, researchers are exploring new strategies to detect and characterize these elusive worlds using advanced telescopes such as the Webb telescope.

If habitable planets are found to exist around white dwarfs, it would significantly broaden the range of environments where life might persist, demonstrating that planetary systems may remain viable hosts for life even long after the death of their host star.

Adapted from an article originally published in The Conversation.

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“Coordinating mineral detections from orbit at Mars with in situ detections by the Perseverance rover gives us a detailed look at ancient chemical reactions for a few small areas and a broader view across kilometers of the surface,” said Bishop.

After landing, Perseverance headed west, analyzing surface materials with its suite of instruments and collecting samples of the most interesting ones for eventual return to Earth. Near the landing site, the rover identified basaltic rocks rich in olivine and pyroxene. Then, as it traveled toward a western delta, it found layers and clays and carbonates, confirming observations from orbit. Perseverance’s instruments were able to examine these smectite clays and carbonates directly, at a much finer mm to cm scale than CRISM.

Perseverance discovered unusual millimeter-scale nodules of iron phosphate and iron sulfide embedded in clay-rich mudstone near Neretva Vallis, at the Bright Angel and Masonic Temple sites (Hurowitz et al., 2025). The juxtaposition of the tiny, green-toned specks of chemically reduced iron against the reddish mudstone matrix prompted further study with the rover’s instruments. Phosphates are significant because they play a key role in biology on Earth. Analyses revealed that the mudstone is primarily composed of smectite clays (such as montmorillonite and nontronite), ferric oxides and hydroxides (including hematite and goethite), and calcium sulfates (such as gypsum and bassanite). Interestingly, the reduced minerals appear more abundant where the surrounding mudstone is less oxidized and where organic compounds are more concentrated, based on Raman spectral data. This relationship suggests that organic material may have directly influenced these unusual redox reactions.

“My group observed redox reactions in lab experiments where ferrihydrite containing oxidized iron was heated with organic compounds, including amino acids, to produce the mineral magnetite containing reduced iron,” said Bishop.

Redox reactions are chemical processes where minerals gain or lose electrons, creating energy that can sometimes be used by living organisms. Amino acids are the building blocks of life as we know it and may also have played a role in prebiotic chemistry through interactions with minerals. Data from Perseverance’s SHERLOC instrument (Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals) suggest that organic compounds at Jezero Crater probably interacted with a variety of minerals on ancient Mars (Scheller et al., 2022).

The greenish specks are likely the mineral vivianite, a phosphate that can change its chemistry when exposed to different environmental conditions. Perseverance also found phosphate minerals at another site, Onahu, where evidence suggests they were once vivianite that later oxidized, or “rusted.” A separate study of Jezero crater sediments revealed alternating colored layers caused by shifts in iron chemistry, showing that Mars’ environment changed over time in ways that could have influenced habitability.

Identifying specific minerals on Mars is key to reconstructing the ancient geochemical environments that once shaped the planet.

“Spectral analyses of pure minerals and mineral mixtures in the laboratory are necessary for interpreting the spectral data collected at Mars,” said Bishop.

At the SETI Institute, Bishop’s group conducts laboratory experiments on minerals such as phyllosilicates, sulfates, carbonates, and phosphates. These studies provide the foundation for recognizing and characterizing Martian minerals, both from orbit with the CRISM imager and directly on the surface through near-infrared spectra measured by Perseverance’s SuperCam instrument.

However, Mars’s atmosphere and some instrument quirks can distort CRISM’s hyperspectral data, making orbital mineral identification tricky even after standard processing. Itoh and Parente (2021) addressed this problem using the most advanced method yet for correcting and de-noising CRISM data. Earlier processing pipelines still left residual artifacts and noise. The new approach finds and removes those lingering distortions (from Martian gas absorption bands, sensor temperature drifts, or even icy haze), while simultaneously filtering out random noise in each image.

“By extracting the atmosphere’s imprint directly from the image itself, our technique yields cleaner surface spectra,” said Parente. “This approach effectively eliminates the need for manual fixes like spectral ratioing, which scientists used to rely on to cancel out calibration quirks but which risked altering the surface signals and causing misidentification of minerals. With CRISM data now clarified by this method, subtle mineral features once lost in the ‘static’ can be detected with greater confidence.”

Building on this leap in data quality, a companion study by Saranathan and Parente (2021) used AI to turn those cleaned-up spectra into the most accurate mineral maps of Mars to date. The new approach trains a Generative Adversarial Network (GAN) to automatically learn distinctive spectral “fingerprints” of various minerals from CRISM data. In this GAN-derived representation space, even subtle differences between mineral signatures stand out, and simple similarity metrics can reliably match each pixel to its likely mineral identity. The study produced a map of dominant mineralogy that pinpoints the distribution of materials such as carbonates, clays, and pyroxenes with unprecedented clarity and minimal ambiguity. Parente and his team released a map of Jezero Crater’s mineral diversity, successfully identifying known mineral deposits and revealing small mineral outcrops that earlier mapping approaches had overlooked (Parente et al, 2021).

By sharpening the view from orbit, these innovations enabled Mars scientists to improve their understanding of the planet’s ancient geochemical environment.

On Earth, microorganisms commonly interact with minerals in ways that transform their chemistry. For example, researchers have observed that microbes in cold, oxygen-free Antarctic lakes can convert sulfates (containing oxidized sulfur) into sulfides (containing reduced sulfur) (Bishop et al., 2003). While there is no evidence for microbes on Mars today, if life once existed there, similar processes could have reduced sulfate minerals to sulfides in an ancient lake at Jezero crater. On Earth, bacteria also promote the formation of the phosphate mineral vivianite by reducing iron in oxygen-poor swamps rich in phosphate ions. However, given the long geologic timescales on Mars, the tiny pockets of reduced vivianite and sulfides found within oxidized mudstones at Jezero were more likely formed by non-biological processes — for example, chemical reactions involving organic compounds.

“Sulfur isotope analyses were used on the Antarctic sediments to determine a biologic origin of the tiny sulfide crystals in anoxic water,” said Bishop.

Scientists could gain valuable clues about the geochemical processes that shaped these Martian minerals by running similar sulfur isotope tests on the Bright Angel samples when they return to Earth.

Perseverance’s samples from the Bright Angel and Masonic Temple sites show the potential for complex chemistry on ancient Mars and raise new questions about the redox reactions that created these unusual minerals. Once these cached samples return to Earth, scientists will be able to study them with far more powerful laboratory techniques, revealing finer details about mineral identities, spatial arrangements, and the geochemical processes that shaped them. Such analyses could not only clarify Mars’ chemical history but also shed light on the potential for prebiotic — or even biological — chemistry beyond our own planet.